How to add buttons from "Overlay" section in custom panel?
I think the problem is trying to add settings for the 3D view outside the 3D view.You can place it in the Sidebar.

import bpy

class HelloWorldPanel(bpy.types.Panel):
    """Creates a Panel in the Object properties window"""
    bl_label = "Hello World Panel"
    bl_idname = "OBJECT_PT_hello"
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'UI'

    def draw(self, context):
        layout = self.layout

        overlay = bpy.context.space_data.overlay

        row = layout.row()
        row.prop(overlay, "normals_length")

def register():
    bpy.utils.register_class(HelloWorldPanel)


def unregister():
    bpy.utils.unregister_class(HelloWorldPanel)


if __name__ == "__main__":
    register()